Technical Field
[0001] The present invention relates to a direct fuel injection-type spark ignition internal
combustion engine.
Background Art
[0002] In a homogeneous combustion by forming a homogeneous mixture in a cylinder and by
igniting and burning the homogeneous mixture at an ignition timing in the last stage
of the compression stroke, if a tumbling flow is formed in the cylinder by the intake
air fed into the cylinder, disturbance due to the tumbling flow is made present in
the cylinder at the ignition timing by sustaining the tumbling flow up to the ignition
timing in the last stage of the compression stroke, and the combustion speed of the
homogeneous mixture is increased by the disturbance, then a good homogeneous combustion
can be realized.
[0003] In order to sustain the tumbling flow up to the ignition timing in the last stage
of the compression stroke, there have been proposed direct fuel injection-type spark
ignition internal combustion engines for forming a strong tumbling flow in a cylinder
by arranging an intake flow control valve in the intake port and by feeding the intake
air through the intake flow control valve into the cylinder along the upper wall of
the intake port (see, for example,
JP-A-2005-180247,
JP-A-2004-190548 and
JP-A-2002-227651).
[0004] In the above direct fuel injection-type spark ignition internal combustion engines,
when the intake air is to be fed through the intake flow control valve into the cylinder
along the upper wall of the intake port, the intake port is throttled by the intake
flow control valve. Therefore, a strong tumbling flow can be formed in the cylinder
without any particular problem when the required intake air amount is relatively small.
When the required intake air amount becomes relatively large, however, the intake
air becomes in short supply if the intake port is throttled by the intake flow control
valve. Therefore, a strong tumbling flow cannot be formed in the cylinder by using
the intake flow control valve.
[0005] In the homogeneous combustion in which the air-fuel ratio of a homogeneous mixture
is leaner than the stoichiometric air-fuel ratio, the intake air is required in a
relatively large amount. At this time, if a strong tumbling flow cannot be formed
in the cylinder, the combustion speed becomes very slow and it becomes difficult to
obtain a desired engine output.
[0006] Even when the homogeneous mixture has an air-fuel ratio which is the stoichiometric
air-fuel ratio or a rich air-fuel ratio, it is desirable that the combustion speed
is quickened by the disturbance in the cylinder. Namely, if a strong tumbling flow
can be formed in the cylinder without the need of providing the intake flow control
valve, then the engine intake system may not become complex.
[0007] Furthermore, a direct fuel injection type spark ignition internal combustion engine
according to the preamble of claim 1 is disclosed in
EP 1 302 635 A2.
[0008] It is therefore an object of the present invention to provide a direct fuel injection-type
spark ignition internal combustion engine which is capable of forming, in the cylinders
thereof, a strong tumbling flow without the need of using intake flow control valves.
Disclosure of the Invention
[0009] According to the direct fuel injection-type spark ignition internal combustion engine
of the present invention described in claim 1, most of the injected fuel is directed
to a one-fifth portion of the lower side of the cylinder bore wall on the exhaust
valve side in the last stage of the intake stroke, so that a tumbling flow that whirls
in the cylinder descending in the cylinder bore on the exhaust valve side and ascending
in the cylinder bore on the intake valve side, is intensified by the fuel that is
injected from the fuel injection valve arranged nearly at the center in the upper
part of the cylinder toward the exhaust valve side in the cylinder bore in the last
stage of the intake stroke. With the fuel being injected aslant and downward toward
the exhaust valve side in the cylinder bore from the fuel injection valve arranged
nearly at the center in the upper part of the cylinder, the piercing force of the
injected fuel intensifies the tumbling flow that is moving aslant and downward along
the exhaust valve side of the pent roof-type cylinder head, and the component of the
piercing force of the injected fuel in the vertical direction intensifies the tumbling
flow that is descending in the vertical direction along the cylinder bore. With most
of the fuel injected aslant and downward being directed to one-fifth portion of the
lower side of the cylinder bore wall on the exhaust valve side in the last stage of
the intake stroke, the injected fuel favorably works to intensify the tumbling flow
over a long distance until arriving at the cylinder bore wall. Besides, while traveling
over a long distance, the injected fuel vaporizes just before arriving at the cylinder
bore wall and hardly deposits on the cylinder bore wall. Therefore, the engine oil
is hardly diluted, and there is almost no increase in the amount of the unburned fuel
in the exhaust gas that stems from the vaporization of the deposited fuel.
[0010] According to the direct fuel injection-type spark ignition internal combustion engine
of the invention described in claim 2, in the direct fuel injection-type spark ignition
internal combustion engine described in claim 1, the fuel injection valve has a slit
injection hole of a partly arcuate shape, and the horizontal sectional shape of the
fuel injected from the fuel injection valve is nearly symmetrical relative to the
central vertical plane of the cylinder in parallel with the direction of whirl of
the tumbling flow and is a partly arcuate shape being curved inward of the cylinder
bore. Most of the injected fuel having the above sectional shape can be easily directed
to one-fifth portion on the lower side of the cylinder bore wall on the exhaust valve
side in the last stage of the intake stroke, and is used to favorably intensity the
tumbling flow over a predetermined width with the central vertical plane of the cylinder
as a center.
[0011] According to the direct fuel injection-type spark ignition internal combustion engine
of the invention described in claim 3 which is concerned to the direct fuel injection-type
spark ignition internal combustion engine described in claim 2, the partly arcuate
shape is a semi-arcuate shape. Therefore, the tumbling flow can be favorably intensified
over the full width thereof by the injected fuel.
[0012] According to the direct fuel injection-type spark ignition internal combustion engine
of the invention described in claim 4, in the direct fuel injection-type spark ignition
internal combustion engine described in claim 1, the fuel injection valve has a slit
injection hole of the shape of a polygonal line, and the horizontal sectional shape
of the fuel injected from the fuel injection valve is nearly symmetrical relative
to the central vertical plane of the cylinder in parallel with the direction of whirl
of the tumbling flow and is of the shape of a line having a narrow angle not larger
than 180° inward of the cylinder bore. Most of the injected fuel having the above
sectional shape can be easily directed to one-fifth portion on the lower side of the
cylinder bore wall on the exhaust valve side in the last stage of the intake stroke,
and is used to favorably intensify the tumbling flow over a predetermined width with
the central vertical plane of the cylinder as a center.
[0013] According to the direct fuel injection-type spark ignition internal combustion engine
of the invention described in claim 5, in the direct fuel injection-type spark ignition
internal combustion engine described in claim 1, the fuel injection valve has a plurality
of round injection holes, and the horizontal sectional shape of the fuel injected
from the fuel injection valve is nearly symmetrical relative to the central vertical
plane of the cylinder in parallel with the direction of whirl of the tumbling flow
and forms a plurality of nearly round shapes aligned in a partly arcuate shape being
curved inward of the cylinder bore. Most of the injected fuel having the above sectional
shape can be easily directed to one-fifth portion on the lower side of the cylinder
bore wall on the exhaust valve side in the last stage of the intake stroke, and is
used to favorably intensity the tumbling flow in a plurality of portions over a predetermined
width with the central vertical plane of the cylinder as a center.
[0014] According to the direct fuel injection-type spark ignition internal combustion engine
of the invention described in claim 6, in the direct fuel injection-type spark ignition
internal combustion engine described in claim 1, the fuel injection valve has a plurality
of round injection holes, and the horizontal sectional shape of the fuel injected
from the fuel injection valve is nearly symmetrical relative to the central vertical
plane of the cylinder in parallel with the direction of whirl of the tumbling flow
and forms a plurality of nearly round shapes aligned like a line having a narrow angle
not larger than 180° inward of the cylinder bore. Most of the injected fuel having
the above sectional shape can be easily directed to one-fifth portion on the lower
side of the cylinder bore wall on the exhaust valve side in the last stage of the
intake stroke, and is used to favorably intensity the tumbling flow in a plurality
of portions over a predetermined width with the central vertical plane of the cylinder
as a center.
[0015] According to the direct fuel injection-type spark ignition internal combustion engine
of the invention described in claim 7, in the direct fuel injection-type spark ignition
internal combustion engine described in claim 1, the fuel injected from the fuel injection
valve has such a piercing force that the end of fuel 1 ms after the start of injection
reaches not less than 60 mm from the injection hole of the fuel injection valve, and
has a Sauter mean diameter of not larger than 15 µm at a position 60 mm from the injection
hole of the fuel injection valve 2 ms after the start of injection. The tumbling flow
can be favorably intensified by the injected fuel of a large piercing force being
finely atomized to push the tumbling flow over an increased area.
[0016] According to the direct fuel injection-type spark ignition internal combustion engine
of the invention described in claim 8, in the direct fuel injection-type spark ignition
internal combustion engine described in claim 7, the fuel injected from the fuel injection
valve has such a piercing force that the end of fuel 1 ms after the start of injection
reaches not less than 100 mm from the injection hole of the fuel injection valve,
and has a Sauter mean diameter of not larger than 9µm at a position 100 mm from the
injection hole of the fuel injection valve 2 ms after the start of injection. The
tumbling flow can be favorably intensified by the injected fuel of a large piercing
force being finely atomized to push the tumbling flow over an increased area.
Brief Description of the Drawings
[0017]
Fig. 1 is a vertical sectional view schematically illustrating an explanatory example
of a direct fuel injection-type spark ignition internal combustion engine;
Fig. 2 is a bottom view of a cylinder head of Fig. 1;
Fig. 3 is an enlarged view of an ignition plug of Fig. 2;
Fig. 4 is a schematic sectional view illustrating a modified example of the explanatory
example of Fig. 1 in the last stage of the intake stroke;
Fig. 5 is a schematic vertical sectional view illustrating another explanatory example
of the direct fuel injection-type spark ignition internal combustion engine in the
last stage of the intake stroke;
Fig. 6 is a schematic vertical sectional view of the explanatory example of Fig. 5
at the ignition timing;
Fig. 7 is a schematic vertical sectional view illustrating a further explanatory example
of the direct fuel injection-type spark ignition internal combustion engine at the
ignition timing;
Fig. 8 is a sectional view along A-A in Fig 7;
Fig. 9 is a schematic vertical sectional view illustrating a still further explanatory
example of the direct fuel injection-type spark ignition internal combustion engine
at the ignition timing;
Fig. 10 is a sectional view along B-B in Fig 9;
Fig. 11 is a schematic vertical sectional view illustrating an embodiment of the direct
fuel injection-type spark ignition internal combustion engine according to the invention
in the last stage of the intake stroke;
Fig. 12 is a sectional view along D-D in Fig 11;
Fig. 13 is a view illustrating a modified example of the shape of the injected fuel
of Figs. 11 and 12;
Fig. 14 is another sectional view along D-D in Fig 11;
Fig. 15 is a view illustrating a modified example of the shape of the injected fuel
of Fig. 14;
Fig. 16 is a graph illustrating a change in the engine output relative to the direction
of fuel injection; and
Fig. 17 is a graph illustrating a change in the amount of HC emission relative to
the direction of fuel injection.
Best Mode for Carrying Out the Invention
[0018] Fig. 1 is a vertical sectional view schematically illustrating an explanatory example
of a direct fuel injection-type spark ignition internal combustion engine.
[0019] Fig. 2 is a bottom view of a cylinder head of the direct fuel injection-type spark
ignition internal combustion engine of Fig. 1. In these drawings, 1 is a fuel injection
valve arranged nearly at the center in the upper part of the cylinder and injects
the fuel directly into the cylinder, and 2 is an ignition plug arranged near the fuel
injection valve 1. Reference numeral 3 denotes a piston, 4 denotes a pair of intake
valves, and 5 denotes a pair of exhaust valves.
[0020] In the direct fuel injection-type spark ignition internal combustion engine, a homogeneous
mixture leaner than the stoichiometric air-fuel ratio is formed in the cylinder, and
the mixture is ignited by the ignition plug 2 and burns to execute the homogeneous
combustion. During a high engine speed and high engine load operation where a large
output is required, the homogeneous combustion may be executed at the stoichiometric
air-fuel ratio or at a rich air-fuel ratio. In executing the homogeneous combustion
at a lean air-fuel ratio in particular, a desired engine output is not obtained unless
the combustion speed is increased by existence of the turbulence in the cylinder at
the ignition timing. It is, therefore, desired to form, in the cylinder, a tumbling
flow T that descends in the cylinder bore on the exhaust valve side and ascends on
the intake valve side utilizing the intake air that is fed into the cylinder in the
intake stroke and to sustain the tumbling flow T up to the ignition timing in the
last stage of the compression stroke so that the turbulence exists in the cylinder
at the ignition timing.
[0021] Unless the shape and arrangement of the intake port are contrived so as to increase
the thickness of the cylinder head or an intake flow control valve is provided in
the intake port, however, the tumbling flow that is formed in the cylinder is not,
usually, so strong. Even by forming a cavity 3a of a partly arcuate shape in cross
section in the top surface of the piston 3 to suppress the attenuation of the tumbling
flow as in this explanatory example, the tumbling flow attentuates during the compression
stroke and easily extinguishes before the ignition timing; i.e., the turbulence based
on the tumbling flow cannot exist in the cylinder at the ignition timing. In this
explanatory example, therefore, the tumbling flow T which is formed in the cylinder
during the intake stroke but is not so strong is intensified by utilizing the piercing
force of the fuel F injected from the fuel injection valve 1 toward the exhaust valve
side in the cylinder bore in the last stage of the intake stroke. The thus intensified
tumbling flow is favorably sustained up to the ignition timing in the last stage of
the compression stroke to make the turbulence exist in the cylinder.
[0022] The spark plug 2 is arranged on the intake valve side away from the fuel injection
valve 1 that injects the fuel toward the exhaust valve side of the cylinder bore.
Therefore, the fuel injected from the fuel injection valve 1 does not come into direct
collision with the ignition plug 2. Accordingly, the spark plug 2 is not wet with
the fuel, and the occurrence of arc is not hindered.
[0023] In this explanatory example, the fuel injection valve 1 has a slit-like injection
hole, and injects the fuel in nearly the shape of a fan having a relatively small
thickness, wherein the plane at the center of thickness of the fuel spray F is almost
in agreement with a vertical plane P that passes through the center axis of the cylinder
in parallel with the tumbling flow T. Therefore, the fuel F is injected into a space
S in parallel with the vertical plane P between the two intake valves 4, travels,
first, chiefly through the space S between the two intake valves 4 while whirling
in the cylinder together with the tumbling flow T, and hardly deposits on the intake
valves 4 that are opened. If the fuel deposits on the intake valves 4, the intake
air amount often decreases. The above fuel injection into the space S, however, suppresses
the deposition on the intake valves 4.
[0024] Fig. 3 is an enlarged view of the ignition plug 2 of Fig. 2. As shown, the ignition
plug 2 has a center electrode 2a and an L-shaped plate electrode 2b. In this embodiment,
the ignition plug 2 is so arranged that the direction of width of the plate electrode
2b is nearly in parallel with the tumbling flow. Therefore, the tumbling flow is suppressed
from being attenuated by the collision with the plate electrode 2b that occurs when
the direction of width of the plate electrode 2b faces the tumbling flow T (that occurs
when the ignition plug is arranged being turned counterclockwise or clockwise by 90
degrees with respect to the ignition plug arrangement of Fig. 3).
[0025] In this ignition plug arrangement, the direction of thickness of the plate electrode
2b faces the tumbling flow T. However, the thickness of the plate electrode 2b is
so small that the tumbling flow T is hardly attenuated. The same effect can be obtained
not only from the ignition plug arrangement of Fig. 3 but also from the ignition plug
arrangement that is turned by 180 degrees. Further, some ignition plugs may have two
plate electrodes opposed to each other. In this case, too, it is desired that the
direction of thickness of the two plate electrodes is opposed to the tumbling flow
T, and the direction of width thereof is nearly in parallel with the tumbling flow.
[0026] Owing to the above-mentioned arrangement of the ignition plug 2, the arc that generates
across the two electrodes 2a and 2b at the ignition timing is easily drawn by the
tumbling flow T toward the downstream of the tumbling flow enabling the homogeneous
mixture in the cylinder to be easily ignited. On the other hand, as the tumbling flow
in the cylinder becomes stronger at the ignition timing, the arc is drawn and tends
to be extinguished. It is desired to increase the ignition energy with an increase
in the strength of the tumbling flow T in the cylinder at the ignition timing, i.e.,
with an increase in the tumbling flow T intensified by the fuel injection in the last
stage of the intake stroke, so that the arc will not be extinguished even if the arc
is drawn out. As the tumbling flow in the cylinder becomes strong at the ignition
timing, further, the arc tends to be blown out by the tumbling flow. An increased
ignition energy is effective in suppressing the blow-out by the tumbling flow.
[0027] In order to execute the homogeneous combustion at a desired air-fuel ratio, the fuel
injection valve 1 injects the fuel of a required amount in the last stage of the intake
stroke (for example, the crank angle for starting the fuel injection is set depending
upon the amount of fuel injection in a manner that the crank angle for ending the
fuel injection is near the bottom dead center in the intake stroke, or the crank angle
for starting the fuel injection is set in the latter half of the intake stroke irrespective
of the amount of fuel injection). Thus, the tumbling flow T is more intensified with
an increase in the required amount of fuel.
[0028] However, if the tumbling flow is excessively intensified, the combustion speed excessively
increases and, besides, the ignition energy must be increased, so that the arc will
not be blown out by the tumbling flow or that the arc will not be extinguished. Therefore,
it is not desired to unnecessarily intensify the tumbling flow. When the fuel is required
in large amounts, therefore, part of the fuel may be injected in the intermediate
stage or in the initial stage of the intake stroke (or may be injected being divided
into a plurality of times) so that the fuel is injected in a decreased amount in the
last stage of the intake stroke so as to control the degree of intensifying the tumbling
flow T such that the tumbling flow T is not excessively intensified.
[0029] The direct fuel injection-type spark ignition internal combustion engine of this
embodiment executes the homogeneous combustion relying upon the fuel that is directly
injected into the cylinder and is, therefore, capable of reliably feeding the fuel
of a required amount into the cylinder. On the other hand, in the case where the fuel
is injected into the intake port, the fuel has to be injected in an amount in excess
of the required amount to compensate for the deposition of fuel on the wall surface
of the intake port. Further, the direct fuel injection-type spark ignition internal
combustion engine may inject the fuel in the latter half of the compression stroke
during, for example, the low engine load operation to execute the stratified charge
combustion forming the mixture near only the ignition plug 2. In this case, the cavity
3a formed in the top surface of the piston 3 is deviated toward the side of the exhaust
valves 4, and the injected fuel is collected by the cavity near the ignition plug
2.
[0030] In this embodiment, the fuel injection valve 1 injects fuel in nearly the shape of
a fan having a relatively small thickness, which, however, is not to limit the invention,
as a matter of course. The shape of the fuel spray can be arbitrarily set, for example,
in a solid or hollow conical shape, or in a solid pole shape. Further, the fuel spray
may be of an arcuate shape in cross section having a relatively small thickness or
may be of the shape of a line in cross section by using an arcuate slit injection
hole or a combination of a plurality of linear slit injection holes. The fuel spray
may have a relatively large piercing force so as to accelerate the tumbling flow in
the cylinder. Desirably, the fuel may be injected into the above-mentioned space between
the two intake valves.
[0031] Fig. 4 is a schematic sectional view illustrating a modified example of the explanatory
example of Fig. 1. Described below are only the differences from the explanatory example
of Fig. 1. In the modified example, no cavity is formed in the top surface of the
piston 3', and a protuberance 3a' is formed on the intake valve side. This enhances
the compression ratio. A deflection surface 3b' continuing smoothly to the top surface
of the piston 3' is formed on the exhaust valve side of the protuberance 3a'. The
deflection surface 3b' shown in Fig. 4 is partly of an arcuate shape in cross section,
which, however, may be of a linear shape. The tumbling flow T descending in the cylinder
bore on the exhaust valve side and traveling along the top surface of the piston 3',
is deflected by the deflection surface 3b' so as to ascend in the cylinder bore on
the intake valve side. This suppresses the attenuation of the tumbling flow T as in
the explanatory example of Fig 1, so as to easily sustain the tumbling flow up to
the ignition timing.
[0032] Fig. 5 is a schematic vertical sectional view illustrating another explanatory example
of the direct fuel injection-type spark ignition internal combustion engine. Described
below are only differences from the explanatory example of Fig. 1. In this explanatory
example, too, a fuel injection valve 10 is arranged nearly at the center in the upper
part of the cylinder to directly inject the fuel into the cylinder, and the tumbling
flow T which is formed in the cylinder in the intake stroke is not so strong and is
intensified as shown in Fig. 5 by utilizing the piercing force of the fuel F' injected
toward the exhaust valve side of the cylinder bore from the fuel injection valve 10
in the last stage of the intake stroke. The thus intensified tumbling flow is favorably
sustained up to the ignition period in the last stage of the compression stroke to
make the turbulence present in the cylinder.
[0033] An ignition plug 20 is arranged on the exhaust valve side away from the fuel injection
valve 10, and a cavity 30a is formed in the top surface of the piston 30 being deviated
toward the exhaust valve side to suppress the attenuation of the tumbling flow. The
exhaust valve side of the cavity 30a is smoothly continuous to the piston top surface
through a fillet 30b to minimize the attenuation at the time when the tumbling flow
enters into the cavity 30a. In other explanatory examples, too, it is desired that
the above fillet is formed on the exhaust valve side of the cavity where the tumbling
flow flows in.
[0034] Fig. 6 is a schematic vertical sectional view of the explanatory example at the ignition
timing. As shown, the ignition gap g of the ignition plug 20 is positioned near the
center axis c (which is not necessarily in parallel with the center axis of the cylinder
bore but is tilted relative to the center axis of the cylinder bore in this embodiment)
of the cavity 30a. Therefore, the mixture in the cavity starts burning from near the
center thereof due to the arc generated in the ignition gap g of the ignition plug
20, the flame thereof radially propagates to the outer periphery thereof and, finally,
the outer periphery burns nearly simultaneously. Therefore, the two-dimensional flame
propagation distance until the completion of combustion becomes short, and the combustion
speed increases.
[0035] The shape of the cavity 30a can be arbitrarily selected if it has a smooth sectional
shape (e.g., partly arcuate shape in cross section) suppressing the attenuation of
the tumbling flow. Desirably, the cavity 30a has partly spherical shape with the ignition
gap g of the ignition plug 20 nearly as the center at the ignition timing. Therefore,
the arc that generates at the ignition gap g of the ignition plug 20 propagates three-dimensionally
and radially to the mixture in the cavity 30a and, finally, the portions near the
wall surface of the cavity 30a burns simultaneously and completely. This shortens
the nearly practically three-dimensional flame propagation distance until the completion
of combustion and, further, increases the combustion speed.
[0036] Fig. 7 is a schematic vertical sectional view illustrating a further explanatory
example of the direct fuel injection-type spark ignition internal combustion engine
at the ignition timing, and Fig. 8 is a sectional view along A-A in Fig. 7. Described
below are only the differences from the explanatory example of Fig. 1. This explanatory
example is of the two intake valve type like the explanatory example of Fig. 1. In
this case, two tumbling flows in parallel with each other are, first, formed in the
cylinder via two intake valves.
[0037] In the explanatory example of Fig. 1, these two tumbling flows readily combine to
form a single tumbling flow. In this explanatory example, however, the two tumbling
flows whirl in parallel with each other in the cylinder descending in the cylinder
bore on the exhaust valve side and ascending in the cylinder bore on the intake valve
side and are respectively, intensified by the fuel injected in two directions toward
the exhaust valve side of the cylinder bore from the fuel injection valve 1' in the
last stage of the intake stroke, and two cavities 31a and 31b of partly arcuate shape
in cross section are formed in the top surface of the piston 31, which cavities correspond
to the respective tumbling flows. Therefore, the two tumbling flows are sustained
up to the ignition period so that turbulence is present in the respective cavities
31a and 31b and in spaces over the cavities 31a and 31b. To intensify the two tumbling
flows by the injection of fuel in the last stage of the intake stroke, two fuel injection
valves 1" may be arranged between the intake valves and the exhaust valves in the
periphery of upper part of the cylinder as indicated by dot-dash chain lines in Fig.
8; i.e., the two tumbling flows are intensified by the fuel injected toward the exhaust
valve side of the cylinder bore from the fuel injection valves 1", which fuel injections
correspond to the tumbling flows in the last stage of the intake stroke.
In the explanatory exmaple, a bulging portion 31c is formed on the top surface of
the piston 31 between the two cavities 31a and 31b, and the ignition gap g of the
ignition plug 2 arranged nearly at the center in the upper part of the cylinder faces
the top surface 31d of the bulging portion 31c. The bulging portion 31c works to increase
the compression ratio enabling the engine output to increase, the mixture in the cylinder
starts slowly burning from a relatively narrow space between the ignition plug 2 and
the top surface 31d of the bulging portion 31c due to the arc generated in the ignition
gap g of the ignition plug 2, and the flame thereof propagates into the cavities 31a
and 31b on both sides of the bulging portion 31c finally triggering a rapid combustion,
producing little knocking.
[0038] Fig. 9 is a schematic vertical sectional view illustrating a still further explanatory
example of the direct fuel injection-type spark ignition internal combustion engine
at the ignition timing, and Fig. 10 is a sectinal view along B-B in Fig. 9. Described
below are only the differences from the explanatory example of Fig. 1. In this explanatory
example as in the explanatory example of Fig. 1, a tumbling flow that descends in
the cylinder bore on the exhaust valve side and ascends in the cylinder bore on the
intake valve side, is intensified by the fuel injected from the fuel injection valve
1 toward the exhaust valve side of the cylinder bore in the last stage of the intake
stroke, and attenuation of the tumbling flow is suppressed by the cavity 32a of a
partly arcuate shape in cross section formed in the top surface of the piston 32,
so that the tumbling flow is sustained up to the ignition period and that the turbulence
is present in the cylinder.
In the explanatory example, the bulging portions 32b and 32c are formed on the top
surface of the piston 32 on both sides of the cavity 32a. In the explanatory example,
further, two ignition plugs 21 and 22 are arranged between the intake valves and the
exhaust valves in the periphery of the upper part of the cylinder, and ignition gaps
g of the two ignition plugs 21 and 22 are facing the top surfaces 32d and 32e of the
two bulging portions 32b and 32c, respectively. Namely, the two bulging portions 32b
and 32c work to increase the compression ratio enabling the engine output to increase,
the mixture in the cylinder starts slowly burning from two relatively narrow spaces
between the ignition plugs 21, 22 and the top surfaces 32d, 32e of the bulging portions
32b, 32c due to the arc generated in the ignition gaps g of the ignition plugs 21,
22, and the two flames thereof propagate into the cavity 32a between the two bulging
portions 32a and 32c finally triggering a very rapid combustion, increasing the combustion
speed and producing little knocking.
[0039] The disturbance in the cylinder due to the tumbling flow not only makes it possible
to obtain a lean air-fuel ratio but also to improve the combustion by increasing the
combustion speed even in the homogeneous combustion at the stochiometric air-fuel
ratio or at a rich air-fuel ratio. Therefore, if the tumbling flow can be intensified
by injecting the fuel as described above, then no intake flow control valve is necessary
and the engine intake system does not become complex. Fig. 11 is a schematic vertical
sectional view illustrating an embodiment of the direct cylinder fuel injection-type
spark ignition internal combustion engine according to the invention in the last stage
of the intake stroke. In Fig. 11, reference numeral 100 denotes a fuel injection valve
arranged nearly at the center in the upper part of the cylinder, and 2 is an ignition
plug arranged near the intake valve side from the fuel injection valve 100 and is
directed in the same manner as that of the above explanatory example. Reference numeral
6 denotes an intake port communicated with the cylinder via a pair of intake valves
(not shown), and 7 denotes an exhaust port communicated with the cylinder via a pair
of exhaust valves (not shown). Reference numeral 300 denotes a piston.
[0040] Fig. 12 is a sectional view along D-D in Fig 11. Referring to Figs. 11 and 12, a
cavity 300a is formed in the top surface of the piston 300 for suppressing the attenuation
of the tumbling flow T that whirls in the cylinder in the vertical direction descending
in the cylinder bore along the exhaust valve side and ascending along the intake valve
side, the cavity 300a having an arcuate shape in cross section in parallel with the
direction in which the tumbling flow T whirls. In Fig. 12, Ic represents the center
position of the fuel injection valve 100.
[0041] The fuel injection valve 100 has a slit injection hole of a partly arcuate shape.
The fuel f injected from the fuel injection valve 100 in the last stage of the intake
stroke has a horizontal sectional shape which, as represented by solid lines in Fig.
12, is nearly symmetrical relative to the vertical plane P at the center of the cylinder
passing through the center axis of the cylinder in parallel with the direction in
which the tumbling flow T whirls, and is a partly arcuate shape being curved inward
of the cylinder bore. Dot-dash chain lines in Fig. 12 represent a horizontal sectional
shape of the injected fuel f on the side of the fuel injection valve from the D-D
section of Fig. 11. As also shown in Fig. 11, the thickness of the injected fuel f
gradually increases as it goes away from the fuel injection valve 100. Here, the horizontal
direction is a direction perpendicular to the axis of the cylinder and the vertical
direction is a direction in parallel with the axis of the cylinder. In this embodiment,
the partly arcuate shape is, particularly, a semi-arcuate shape. Most of the injected
fuel f having the above sectional shape can be directed a particular range of height
of the cylinder bore wall of the exhaust valve side.
[0042] In the present embodiment and the above-mentioned embodiments, the fuel injected
aslant and downward toward the exhaust valve side of the cylinder bore from the fuel
injection valve arranged nearly at the center in the upper part of the cylinder has
a piercing force that works to reinforce the tumbling flow T that travels aslant and
downward along the pent roof-type cylinder head on the exhaust valve side thereof
and to reinforce the tumbling flow that descends down vertically along the cylinder
bore due to the vertical component of the piercing force.
[0043] Fig. 16 is a graph illustrating a change in the engine output while changing the
direction of injecting the fuel having a semi-arcuate shape in cross section according
to the embodiment. In Fig. 16, (a) represents a case where the injection is directed
to the top surface of the piston near the cylinder bore wall on the exhaust valve
side in the last stage of the intake stroke, (b) represents a case where the injection
is directed to the one-fifth portion on the lower side of the cylinder bore wall height
(H) on the exhaust valve side in the last stage of the intake stroke, (c) represents
a case where the injection is directed to the one-third portion on the lower side
excluding the one-fifth portion on the lower side (i.e., a range from H/5 on the lower
side to H/3 on the lower side) of the cylinder bore wall height (H) on the exhaust
valve side in the last stage of the intake stroke, and (d) represents a case where
the injection is directed to the 4.5/10 portion on the lower side excluding the one-third
portion on the lower side (i.e., a range from H/3 on the lower side to 4.5 H/10 on
the lower side) of the cylinder bore on the exhaust valve side in the last stage of
the intake stroke.
[0044] Though the injected fuel has the same piercing force in all directions of injection,
as shown in Fig. 16, differences occur in the engine output obtained depending upon
the directions of injection, and the greatest engine output is produced in the direction
(b) of injection. Namely, it is considered that the tumbling flow T is intensified
most efficiently in the direction (b) of injection. In order for the injected fuel
to more efficiently intensify the tumbling flow, it is desired that the injected fuel
travels over a long distance in the cylinder and continues to intensify the tumbling
flow T while traveling. In the direction (d) of injection, on the other hand, the
injected fuel comes into collision with the cylinder bore relatively quickly and cannot
efficiently intensify the tumbling flow T. In the direction (a) of injection, the
injected fuel travels over a long distance in the cylinder. In this case, however,
the injected fuel separates away from the cylinder bore and partly passes through
a stagnating space E on the inside of the tumbling flow T or passes through near the
stagnating space E, and cannot efficiently intensify the tumbling flow T.
[0045] Fig. 17 is a graph illustrating a change in the amount of HC emission depending upon
the directions of injection. In the directions (a) and (b) of injection as shown,
the injected fuel travels over a long distance in the cylinder, vaporizes prior to
arriving at the top surface of the piston or the cylinder bore, and hardly deposits
on the top surface of the piston or on the cylinder bore. Namely, it hardly happens
that the deposited fuel is vaporized in the expansion stroke causing an increase in
the amount of emission of unburned HC. On the other hand, the fuel injected in the
direction (d) of injection arrives at the cylinder bore after having traveled over
a relatively short distance in the cylinder and, therefore, deposits on the cylinder
bore in a relatively large amount without being vaporized. The fuel that is deposited
vaporizes in the expansion stroke causing an increase in the amount of emission of
unburned HC. In the direction (c) of injection, too, the fuel travels over a distance
longer than the distance in the direction (d) of injection but travels over a distance
shorter than the distance in the direction (b) of injection. Therefore, the fuel deposits
on the cylinder bore to some extent still causing an increase in the amount of emission
of the unburned HC.
[0046] Upon injecting most part of the fuel from the fuel injection valve 100 onto the band-like
portion over a range of 1/5 (H/5) of the lower side of the cylinder bore wall on the
exhaust valve side (band-like portion in the cylindrical band-like portion 1/5 of
the lower side of the cylinder bore wall on the exhaust valve side from the fuel injection
valve 100) in the last stage of the intake stroke, the tumbling flow T can be favorably
intensified, the injected fuel is suppressed from depositing on the cylinder bore,
the engine oil is hardly diluted, and there is almost no increase in the amount of
unburned fuel in the exhaust gas that stems from the vaporization of the deposited
fuel.
[0047] In this embodiment, further, the fuel injected from the fuel injection valve arranged
nearly at the center in the upper part of the cylinder has a partly arcuate shape
in horizontal cross section nearly symmetrical relative to the central vertical plane
P of the cylinder making it possible to favorably intensify the tumbling flow T over
a predetermined width with the central vertical plane P of the cylinder as a center.
Further, since the partly arcuate shape is a semi-arcuate shape, the tumbling flow
T can be favorably intensified over the whole width.
[0048] Fig. 13 is a horizontal sectional view illustrating a modified example of the shape
of the injected fuel of Figs. 11 and 12. In this modified example, the fuel injection
valve has a plurality of round injection holes, and the horizontal sectional shape
of the fuel injected from the fuel injection valve is of a partly arcuate shape nearly
symmetrical relative to the central vertical plane P of the cylinder in parallel with
the direction in which the tumbling flow whirls as shown in Fig. 13 and forms a plurality
of nearly round shapes aligned partly arcuately being curved inward of the cylinder
bore. The fuel f injected from the round injection holes forms a solid conical shape
which slightly flares downward and aslant. In a horizontal cross section, therefore,
the solid conical shape is traversed aslant and, strictly speaking, the round shapes
become elliptical shapes having a long axis radially extending from the center Ic
of the fuel injection valve.
[0049] Most of the thus injected fuel can be easily directed to the 1/5 portion on the lower
side of the cylinder bore wall on the exhaust valve side in the last stage of the
intake stroke like the injected fuel having a partly arcuate shape in cross section.
Further, the tumbling flow T can be preferably intensified at a plurality of portions
thereof over a predetermined width with the central vertical plane of the cylinder
as a center.
[0050] Fig. 14 is a sectional view which corresponds to Fig. 12 and illustrates another
shape of the injected fuel. The fuel injection valve for injecting the fuel of this
shape has a slit injection hole of the shape of a line, and the injected fuel has
a horizontal sectional shape of a line which is nearly symmetrical relative to the
central vertical plane P of the cylinder and has a contained angle TH smaller than
180° inward of the cylinder bore. Most of the injected fuel having the above sectional
shape can also be easily directed to the 1/5 portion on the lower side of the cylinder
bore wall on the exhaust valve side in the last stage of the intake stroke. Further,
the tumbling flow T can be preferably intensified over a predetermined width with
the central vertical plane of the cylinder as a center.
[0051] Fig. 15 is a horizontal sectional view illustrating a modified example of the shape
of the injected fuel of Fig. 14. In this embodiment, the fuel injection valve has
a plurality of round injection holes, and the fuel injected from the fuel injection
valve has a horizontal sectional shape which is a line nearly symmetrical relative
to the central vertical plane P of the cylinder as shown in Fig. 15, and forms a plurality
of nearly round shapes (strictly, elliptical shapes as described above) aligned like
a line having a contained angle TH smaller than 180° inward of the cylinder bore.
Most of the injected fuel having the above sectional shape can also be easily directed
to the 1/5 portion on the lower side of the cylinder bore wall on the exhaust valve
side in the last stage of the intake stroke. Further, the tumbling flow T can be preferably
intensified at a plurality of portions thereof over a predetermined width with the
central vertical plane of the cylinder as a center.
[0052] Here, to favorably intensify the tumbling flow T by the injected fuel as described
above, it is desired that the piercing force of the injected fuel is as strong as
possible. It is further desired that the injected fuel is finely atomized to a sufficient
degree while it travels increasing the area that pushes the tumbling flow T. It is
desired that the injected fuel for favorably intensifying the tumbling flow T has
such a piercing force that the end of fuel 1 ms after the start of injection reaches
not less than 60 mm from the injection hole of the fuel injection valve, and has a
Sauter mean diameter of not larger than 15 µm at a position 60 mm from the injection
hole of the fuel injection valve 2 ms after the start of injection.
[0053] Further, the injected fuel for further favorably intensifying the tumbling flow T
has such a piercing force that the end of fuel 1 ms after the start of injection reaches
not less than 100 mm from the injection hole of the fuel injection valve, and has
a Sauter mean diameter of not larger than 9µm at a position 100 mm from the injection
hole of the fuel injection valve 2 ms after the start of injection.
1. Funkenzündungsbrennkraftmaschine der kraftstoffdirekteinspritzenden Bauart mit einem
Kraftstoffeinspritzventil (100), das nahezu an der Mitte in dem oberen Teil des Zylinders
angeordnet ist, und einer Zündkerze (2), die an dem oberen Teil des Zylinders angeordnet
ist, dadurch gekennzeichnet, dass der größte Anteil des eingespritzten Kraftstoffs (f) zu einem Ein-Fünftel-Abschnitt
an der unteren Seite der Zylinderbohrungswand an der Seite des Auslassventils (7)
in der letzten Stufe des Einlasstakts gerichtet ist, sodass ein Walzenstrom (T), der
in dem Zylinder absteigend in der Zylinderbohrung an der Seite des Auslassventils
(7) und aufsteigend in der Zylinderbohrung an der Seite des Einlassventils (6) wirbelt,
durch den Kraftstoff (f) intensiviert wird, der von dem Kraftstoffeinspritzventil
(100) in Richtung der Seite des Auslassventils (7) in der Zylinderbohrung in der letzten
Phase des Einlasstakts eingespritzt wird.
2. Funkenzündungsbrennkraftmaschine der kraftstoffdirekteinspritzenden Bauart gemäß Anspruch
1, wobei das Kraftstoffeinspritzventil (100) ein Schlitzeinspritzloch mit einer teilweise
bogenartigen Form hat, und die Horizontalschnittform des von dem Kraftstoffeinspritzventil
(100) eingespritzten Kraftstoffs (f) nahezu symmetrisch relativ zu der zentralen Vertikalebene
(P) des Zylinders, die parallel zu der Richtung der Verwirbelung der Walzenströmung
(T) ist, und eine teilweise bogenartige Form hat, die einwärts der Zylinderbohrung
gekrümmt ist.
3. Funkenzündungsbrennkraftmaschine der kraftstoffdirekteinspritzenden Bauart gemäß Anspruch
2, wobei die teilweise bogenartige Form eine halbbogenartige Form ist.
4. Funkenzündungsbrennkraftmaschine der kraftstoffdirekteinspritzenden Bauart gemäß Anspruch
1, wobei das Kraftstoffeinspritzventil (100) ein Schlitzeinspritzloch mit der Form
einer Linie hat, und die Horizontalschnittform des von dem Kraftstoffeinspritzventil
(100) eingespritzten Kraftstoffs (f) nahezu symmetrisch relativ zu der zentralen Vertikalebene
(P) des Zylinders ist, die parallel zu der Richtung der Verwirbelung der Walzenströmung
(T) ist, und die Form einer Linie hat, die einen eingeschlossenen Winkel (TH) von
nicht größer als 180 Grad einwärts der Zylinderbohrung hat.
5. Funkenzündungsbrennkraftmaschine der kraftstoffdirekteinspritzenden Bauart gemäß Anspruch
1, wobei das Kraftstoffeinspritzventil (100) eine Vielzahl runder Einspritzlöcher
hat und die Horizontalschnittform des von dem Kraftstoffeinspritzventil (100) eingespritzten
Kraftstoffs (f) nahezu symmetrisch relativ zu der zentralen Vertikalebene (P) des
Zylinders ist, die parallel zu der Richtung der Verwirbelung der Walzenströmung (T)
verläuft, und eine Vielzahl von nahezu runden Formen ausbildet, die in einer teilweise
bogenartigen Form ausgerichtet sind, die einwärts der Zylinderbohrung gekrümmt ist.
6. Funkenzündungsbrennkraftmaschine der kraftstoffdirekteinspritzenden Bauart gemäß Anspruch
1, wobei das Kraftstoffeinspritzventil (100) eine Vielzahl runder Einspritzlöcher
hat, und die Horizontalschnittform des von dem Kraftstoffeinspritzventil (100) eingespritzten
Kraftstoffs (f) nahezu symmetrisch relativ zu der zentralen Vertikalebene (P) des
Zylinders ist, die parallel zu der Richtung der Wirbelung der Walzenströmung (T) verläuft,
und eine Vielzahl von nahezu runden Formen ausbildet, die wie eine Linie ausgerichtet
sind, die einen eingeschlossenen Winkel (TH) von nicht größer als 180 Grad einwärts
der Zylinderbohrung hat.
7. Funkenzündungsbrennkraftmaschine der kraftstoffdirekteinspritzenden Bauart gemäß Anspruch
1, wobei der von dem Kraftstoffeinspritzventil (100) eingespritzte Kraftstoff (f)
eine solche Durchdringungskraft hat, dass das Ende des Kraftstoffs 1 ms nach dem Start
der Einspritzung nicht weniger als 60 mm von dem Einspritzloch des Kraftstoffeinspritzventils
(100) erreicht, und einen Sauter-Durchmesser von nicht mehr als 15 m an einer Stelle
60 mm von dem Einspritzloch des Kraftstoffeinspritzventils (100) 2 ms nach dem Start
der Einspritzung hat.
8. Funkenzündungsbrennkraftmaschine der kraftstoffdirekteinspritzenden Bauart gemäß Anspruch
7, wobei der von dem Kraftstoffeinspritzventil (100) eingespritzte Kraftstoff (f)
eine solche Durchdringungskraft hat, dass das Ende des Kraftstoffs 1 ms nach dem Start
der Einspritzung nicht weniger als 100 mm von dem Einspritzloch des Kraftstoffeinspritzventils
(100) erreicht, und einen Sauter-Durchmesser von nicht mehr als 9 m an einer Stelle
100 mm von dem Einspritzloch des Kraftstoffeinspritzventils (100) 2 ms nach dem Start
der Einspritzung hat.